Networks on chip NOC proved to be scalable interconnect structures in particular for systems on chip which could become possible solutions for future on chip interconnections between so-called IP blocks, i.e. intellectual property blocks. IP blocks are usually modules on chip with a specific function like CPUs, memories, digital signal processors or the like. The IP blocks communicate with each other via the network on chip. The network on chip is typically composed of network interfaces and routers. The network interfaces serve to provide an interface between the IP block and the network on chip, i.e. they translate the information from the IP block to information which the network on chip can understand and vice versa. The routers serve to transport data from one network interface to another. For best effort communication, there is no guarantee regarding the latency of the throughput of the communication. For guaranteed throughput services, an exact value for the latency and throughput is required. In addition, fewer or more communication classes may be present in the network, and be used by the monitoring system.
The communication within a network on chip NOC is typically packet-based, i.e. the packets are forwarded between the routers or between routers and network interfaces. A packet typically consists of a header and payload.
To monitor the data traffic via the network on chip, debug probes can be attached to components of the network on chip, i.e. routers and network interfaces, and may allow a debugging of data to be generated on-chip. The probes can be organized in a monitoring system. A sniffer probe allows (non-intrusive) access to functional data from a network link and/or a NoC component. Sniffer probes can be arranged such that they are able to sniff from a connection passing that link. Sniffing is at least part of the data traffic required for debugging and constitutes a requirement for other debug-related components like analyzers or event-generators and data/event-filters. Data generated by sniffers is sent towards the monitoring service access point (MSA) via a debug connection. The monitoring service access point constitutes a centralized access point for the monitoring data. Monitoring service access points MSAs may be present in the system, and they may located on the system on chip SOC (same or different die), or different (companion) chips (such as FPGA), or even on debugging or prototyping equipment (including PCs that are linked up with the SOC). In order to sniff the whole traffic from a connection, the bandwidth required for the debug connection will correspond to more or a less to the bandwidth of the sniffed connection.
The sniffing or monitoring probes may be used as a pre-requisite of hardware, software or system level debugging or may be provided for a run-time performance analysis. In “An event-based network-on-chip monitoring service” by Ciordas et al., in Proc. Int'l High-Level Design Validation and Test Workshop (HLDVT), November 2004, a generic modular probe has been described. A sniffer is used to monitor the data of a network link and to forward its output data to a monitoring service access point. The monitoring probe typically comprises a sniffer, an event generator and a monitoring network interface. Such a probe can be attached to a router or a network interface. The event generator is used to generate a time-stamped event based on the data from the sniffer. The monitoring network interface is used packetize the data from the event generator and the data is sent via the network-on-chip to the centralized monitoring service access point.
Typically, such monitor may involve a lot of local processing. The required data is sniffed locally, through the generic sniffer, e.g. from the router where the monitor is attached. Other data passing other network on chip elements may be outside the reach of such a monitor. Therefore, if not all the routers probed many cases may occur where monitoring is not possible. However, if the number of monitors are reduced the monitoring visibility on the system may also be reduced.